High-power GaN-based laser with tunnel junction
Thus far, the highest output power measured on GaN-based lasers is about 7W, as shown in the picture.  In comparison, some GaAs-based lasers emit more than 30W in continuous-wave operation at room temperature. A key reason for this difference is the inherently large p-side electrical resistance of GaN-based laser diodes. It leads to strong Joule heating which lowers the gain and boosts various loss mechanisms that eventually cause the typical power roll-off at high currents. 
In search for a possible remedy, we recently simulated the effect of a p/n tunnel junction that replaces most of the p-doped layers by highly conductive n-doped material. First results look quite promising.  As shown by the red lines in the picture, the bias is substantially reduced and the peak lasing power is close to 20W. This simulation assumes a negligible tunnel junction resistance which is not yet accomplished in practical devices.  However, the numerical proof of concept hopefully helps stimulate further research efforts into GaN-based tunnel junctions for application in LEDs and lasers.
 M. Kawaguchi et al., Proc. SPIE 9748 (2016) 974818
 J. Piprek, Compound Semicond. Mag. 23 (2017) no. 5, pp. 34-38
 B. P. Yonkee et al., Opt. Express 24 (2016) 256556